The present invention relates to mounting systems for mounting multi-contact electrical headers or connectors on a printed circuit board and, more particularly, to mounting arrangements which allow a measure of relative movement between the connector or header and its printed circuit board.
In the design of electronic systems involving multiple printed circuit boards, it is common to effect circuit interconnection between the circuit boards by directly plugging one circuit board into another or using cable assemblies to effect the interconnection. In those designs that use cable assemblies, multi-contact headers or connectors are mounted on the various circuit boards and are interconnected with multi-conductor cables. In direct board-to-board type connection systems, a backplane or motherboard is provided with an appropriate number of receptacles for receiving and effecting electrical connection with respective daughterboards to form a complete system. The direct board-to-board system dispenses with the need for interconnection cables and allows the system designer to place as many electrical devices and circuits as is practical on the daughterboards to maximize packaging efficiency. In larger systems, the size of each circuit board can be quite large, for example, up to 24 inches (30 cm.) on a side. In such systems, a large number of circuit interconnections must oftentimes be effected, and, to this end, high density connector systems have been developed which locate the respective pins and receptacles on relatively close centers, for example, 0.050 inches (1.27 mm.) in a multi-row matrix so that several hundred or more circuit connects are possible per header.
In general, the use of a single high density header on a printed circuit board does not entail special mounting considerations. However, where the circuit board is relatively large and the number of circuit connects requires the use of two or more separate headers or connectors on the printed circuit board, problems can be encountered under certain circumstances when mating two printed circuit boards. In such multi-header applications, the printed circuit board manufacturer establishes the position and arrangement of the mounting holes for each header. The dimensional tolerances for each group of mounting holes can accumulate in such a way that the headers in a multi-header application are misaligned relative to their design-specified positions. While the misalignment is typically less than a few thousandth of an inch, the misalignment increases the insertion forces required to effect engagement of the parts and stresses the circuit boards. In extreme situations, the stress may be sufficient to `bow` the circuit board out of it normal plane and may be sufficient to cause `stubbing,` that is, the failure of one or more pins to mate with their respective receptacles and subject the parts to deformation or bending. In addition, the circuit boards, in their ultimate application, can operate at an elevated temperature sufficient to cause physical expansion of the boards. For example, where a circuit board has two or more headers along its edge which mate with corresponding connectors on another circuit board, the spacing between the connectors and their headers can increase somewhat because of changes in the operating temperature. Should it be necessary to disengage a thermally hot circuit board and effect replacement with a circuit board that is at room temperature, the difference in physical size and connector spacing can greatly increase the insertion force and, particularly where small pin center dimensions are used, and can unduly stress the circuit boards and their components.
Various mounting arrangements have been used to address the above problem and accommodate the misalignment. For example, U.S. Pat. No. 4,470,100 to Rebaudo et al. carries the connectors on a bracket that is coupled to its circuit board by a pin-and-slot arrangement that allows a measure of relative movement between the connectors and the circuit board. Electrical connection between the bracket-mounted connector and its circuit board is effected by a flex circuit between the connectors and the circuit board. While such mounting systems, as represented by Rebaudo et al., are effective, they represent a cost increment that limits their application to systems in which cost is not a primary factor.